Negative Ulnar Variance and Kienböck Disease.

PURPOSE: To test the primary null hypothesis that there is no difference in mean ulnar variance (UV) scaled to the length of the capitates between 166 wrists with Kienböck disease and an equal number of matched controls and to test the secondary null hypothesis that mean scaled UV does not vary based on age, sex, or race in both Kienböck and control wrists.

METHODS

Ulnar variance was measured on posteroanterior radiographs of the wrist as the distance between a line through the midpoint between the volar and the dorsal edges of the ulnar margin of the radius and a line tangential to the most distal aspect of the carpal surface of the head of the ulna, both perpendicular to the longitudinal axis of the radius. Measurement of UV was scaled to the length of the capitate, resulting in a UV to capitate height (UV:CH) ratio.

RESULTS

We found a significant difference in mean UV:CH ratio between patients with Kienböck disease and a control group matched by age, sex, race, and limb. The prevalence of negative UV was high in both patients with Kienböck disease and matched controls. There were no differences in mean UV:CH ratio with respect to age, sex, or race among patients with Kienböck disease or matched controls.

CONCLUSIONS

The precise role of ulna minus in the development of Kienböck disease remains uncertain and unanswered, given that many patients with Kienböck disease have neutral or positive UV. In addition, a large proportion of the normal population has negative UV, whereas Kienböck disease is rare.